Implantable device having osseointegrating protuberances

ABSTRACT

An implantable device for mounting to a patient&#39;s bone includes a housing and at least one osseointegrating protuberance. The housing includes a surface having an abutting portion configured to abut the bone when the housing is implanted in the patient, the abutting portion defining a housing axis orthogonal to the surface. The at least one osseointegrating protuberance: extends from the surface of the housing; is adapted to abut the patient&#39;s bone; and has a substantially smooth shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/066,062, filed on Oct. 29, 2013, now abandoned which is acontinuation of U.S. patent application Ser. No. 13/099,927 filed on May3, 2011, now U.S. Pat. No. 8,571,676, which is a divisional of U.S.patent application Ser. No. 10/825,359, filed on Apr. 16, 2004, now U.S.Pat. No. 7,937,156, which claims priority from Australian ProvisionalPatent Application No. 2003901867, filed on Apr. 17, 2003. Each of thesedocuments is hereby incorporated by reference herein.

BACKGROUND

Field of the Invention

The present invention relates generally to implantable devices and, moreparticularly, to implantable devices having osseointegratingprotuberances.

Related Art

Medical devices often include one or more components that arepermanently or temporarily implanted in a patient. Many such implantabledevices are designed to be mounted adjacent to, abutting, or in thesurface of one or more bones. Various techniques have been implementedin order to fix such devices in place and to ensure that the devices donot undergo movement once implanted.

In one conventional approach, an implantable device is the housing for areceiver/stimulator unit has been positioned on a bone within the headof the recipient by drilling a bed or well into and through theposterior section of the mastoid bone lying behind the recipient's ear.Such a bed is usually made by drilling the bone down to the lining ofthe brain or dura mater, so that the receiver/stimulator unit ismaintained in position and does not protrude excessively past the skullsurface. The tight dimensions of the bed or well relative to the size ofthe housing together with the eventual growth of a fibrous capsuleserves to help retain the housing in its desired position. Onedisadvantage of this technique is the time taken in the implant surgeryto create the bed. A further disadvantage is that there is somepotential for the housing to shift out of the well due to an impact tothe head of the recipient. Still further, this technique is not alwayspossible depending upon the thickness of the surrounding bone and theage and anatomy of the recipient.

Another conventional technique has involved the positioning of at leastone suture or Dacron tie (bioresorbable or non-bioresorbable) across thehousing to hold it in place. (DACRON is a trademark of E.I. du Pont deNemours and Company) One problem with this approach is that drilling ofthe holes into the surrounding bone can be a difficult and timeconsuming procedure, and especially for young children, much care mustbe taken by the surgeon to ensure that the drilling does not perforatethe dura mater, as the skull thickness in such cases can be quite thin.Further to this, the suture or Dacron ties may not be sufficientlystrong enough to withstand a substantial impact to a region of the headadjacent the device and as a result, such a force may dislodge thedevice from its desired position. In addition, it has been found that ifa suture or Dacron tie is inadvertently placed across an inappropriatesection of the device, such as across a strain relief of the electrodelead, the suture/tie may cause the lead/device to undergo fatigue andcause failure at this location.

SUMMARY

In one aspect of the present invention, an implantable device formounting to a patient's bone is disclosed. The device comprises ahousing including a surface having an abutting portion configured toabut the bone when the housing is implanted in the patient, the abuttingportion defining a housing axis orthogonal to the surface; and at leastone osseointegrating protuberance extending from the surface of thehousing; the at least one protuberance being adapted to abut thepatient's bone; and the at least one protuberance having a substantiallysmooth shaft.

In another aspect of the present invention, an implantable component ofa tissue stimulating prosthesis is disclosed. The implantable componentcomprises a housing including a surface having an abutting portionconfigured to abut the bone when the housing is implanted in thepatient, wherein the abutting portion defines a housing axis orthogonalto the surface; and one or more components of the prosthesis mounted inthe housing; and at least one osseointegrating protuberance extendingfrom the surface of the housing; the at least one protuberance beingadapted to abut the patient's bone; and the at least one protuberancehaving a substantially smooth shaft.

In a further aspect of the present invention, a method for implanting animplantable device having a housing with an abutting surface configuredto prevent osseointegration of the housing with a patient's bone and atleast one osseointegrating protuberance extending from the housing isdisclosed. The method comprises forming a pocket in the patient's boneto receive the housing; positioning the housing in the pocket such thatthe at least one protuberance is in direct contact with a surface of thepatient's bone forming the pocket; and allowing osseointegration of theat least one protuberance to occur implantable component of a tissuestimulating prosthesis is disclosed. The implantable component comprisesa housing including a surface having an abutting portion configured toabut the bone when the housing is implanted in the patient, wherein theabutting portion defines a housing axis orthogonal to the surface; andone or more components of the prosthesis mounted in the housing; and atleast one osseointegrating protuberance extending from the surface ofthe housing; the at least one protuberance being adapted to abut thepatient's bone; and the at least one protuberance having a substantiallysmooth shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is simplified diagram of a cochlear prosthetic device suitablefor implementing the implantable device housing of the presentinvention.

FIG. 2A is a plan view of one embodiment of an implantable device of thepresent invention.

FIG. 2B is a side view of the implantable device shown in FIG. 2A.

FIG. 2C is an end view of the implantable device in FIG. 2A.

FIG. 2D is a schematic end view of the implantable device shown in FIG.2B.

FIG. 3A is a plan view of another embodiment of an implantable device ofthe present invention.

FIG. 3B is a side view of the implantable device shown in FIG. 3A.

FIG. 3C is an end view of the implantable device shown in FIG. 3A.

FIG. 3D is a schematic end view of the implantable device shown in FIG.3B.

FIG. 4A is a plan view of a further embodiment of an implantable deviceof the present invention.

FIG. 4B is a side view of the implantable device shown in FIG. 4A.

FIG. 4C is an end view of the implantable device shown in FIG. 4A.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to one or moreosseointegrating protrusions extending from surfaces of an implantabledevice to secure the device to a bone. Osseointegration is a termcommonly used to describe the process in which living bone forms abiological bond to an implanted element, firmly securing the implantedelement to the skeletal structure. Osseointegration is thought to occurat a molecular level where the implant becomes part of the bone to whichthe implant has been mounted. There is a tendency for the formation ofthis structural connection to continue over time, further adhering theliving bone to the surface of an implant.

Embodiments of the present invention are described below in connectionwith one type of implantable device, a cochlear prosthetic device.Cochlear prostheses use direct electrical stimulation of auditory nervecells to bypass absent or defective hair cells that normally transduceracoustic vibrations into neural activity. Such devices generally usemulti-contact electrodes inserted into the scala tympani of the cochleaso that the electrodes may differentially activate auditory neurons thatnormally encode differential pitches of sound. Such devices are alsoused to treat a smaller number of patients with bilateral degenerationof the auditory nerve. For such patients, the cochlear prosthetic deviceprovides stimulation of the cochlear nucleus in the brainstem.

Exemplary cochlear prostheses in which the present invention may beimplemented include, but are not limited to, those systems described inU.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894 and 6,697,674.As described therein, cochlear prostheses generally include an external,wearable control unit that determines a pattern of electricalstimulation that is provided to an implanted stimulator unit containingactive circuitry in a hermetic enclosure. Electrical stimulationchannels are routed through electrodes to provide electrical stimulationof auditory nerve cells.

FIG. 1 is a schematic diagram of an exemplary cochlear implant system orprosthetic device 100 in which embodiments of the present invention maybe implemented. In the context of such an application, embodiments ofthe present invention are directed to a carrier member of an electrodearray 104 which has a holding member disposed on the surface thereof forthe surgeon to grasp during insertion or implantation of the electrodearray into the cochlear 122 of a recipient (also referred to herein as apatient).

Once implanted, electrodes 102 of the electrode array 104 receivestimulation signals from a stimulator unit 106. Stimulator unit 106 istypically electrically connected to electrode array 104 by way ofelectrical lead 108. Lead 108 is preferably continuous with noelectrical connectors external the housing of stimulator unit 106.

Stimulator unit 106 is preferably positioned within a housing that isimplantable within the patient. The housing for stimulator unit 106 istypically implantable within a recess in the bone behind the earposterior to the mastoid. When implanted, the housing preferablycontains, in addition to stimulator unit 106, a receiver unit 110.Receiver unit 110 is preferably adapted to receive signals 114 from acontroller 112. Controller 112 is, in use, preferably mounted externalto the body behind the outer ear 120 of the patient such that signals114 are transmitted transcutaneously through the skin of the patient.

Signals 114 travel from controller 112 to receiver unit 110 and viceversa. Receiver unit 110 includes a receiver antenna, such as an antennacoil, adapted to receive radio frequency (RF) signals from acorresponding transmitter antenna 116, such as an antenna coil, wornexternally of the body. The radio frequency signals may comprisefrequency modulated (FM) signals. It should be appreciated that thereceiver antenna may also transmit signals, and that the transmitterantenna may receive such signals. The transmitter antenna coil ispreferably held in position adjacent the implanted location of thereceiver antenna coil by way of respective attractive magnets (notshown) mounted centrally in, or at some other position relative to, thecoils.

External controller 112 comprises a speech processor (not shown) adaptedto receive signals output by a microphone 118. During use, microphone118 is preferably worn on the pinna of the recipient, however, othersuitable locations may be envisaged, such as a lapel of the recipient'sclothing. The speech processor encodes the sound detected by microphone118 into a sequence of electrical stimuli in accordance with speechcoding strategies now or later developed for cochlear implant systems.The encoded sequence is transferred to the implanted receiver/stimulatorunit using the transmitter and receiver antennae. The implantedreceiver/stimulator unit demodulates the signals and allocates theelectrical pulses to the appropriate electrode 102 by an algorithm whichis consistent with the chosen speech coding strategy.

External controller 112 may further comprise a power supply (not shown).The power supply may comprise one or more rechargeable batteries. Thetransmitter and receiver antennae are used to provide power viatranscutaneous induction to the implanted receiver/stimulator unit andthe electrode array.

While cochlear implant system 100 is described as having externalcomponents, in another embodiment, the controller, including themicrophone, speech processor and power supply may also be implantable.In such embodiments, the controller may be contained within ahermetically sealed housing or the housing used for stimulator unit 106.

It should be appreciated that although embodiments of the presentinvention are described herein in connection with cochlear prostheticdevice 100, the same or other embodiments of the present invention maybe implemented in any implantable device now or later developed,including implantable devices included in other tissue-stimulatingprosthetic systems. Examples of such devices include, but are notlimited to, other sensory prosthetic devices, neural prosthetic devices,and functional electrical stimulation (FES) systems. In sensoryprostheses, information is collected by electronic sensors and delivereddirectly to the nervous system by electrical stimulation of pathways inor leading to the parts of the brain that normally process a givensensory modality. Neural prostheses are clinical applications of neuralcontrol interfaces whereby information is exchanged between neural andelectronic circuits. FES devices are used to directly stimulate tissuehaving contractile cells to produce a controlled contraction of thesame.

Generally, the osseointegrating protuberance extends from the housingtoward the bone when the device is in an implant orientation adjacentthe bone. The longitudinal axes of the osseointegrating protuberancesmay lie in a same imaginary plane or be offset from each other, or maybe oriented at an angle relative to an implant axis. The implant axis issubstantially orthogonal with an abutting surfaces of the housing andbone, generally reflecting the direction of motion as the housing isbrought into contact with the bone.

A number of features of the osseointegrating protuberances may beselected to achieve a desired implant objective. For example, apertures,ridges and the like can be included in the osseointegrating protuberanceto effect a more secure retention of the protuberance. In addition tothe physical features of the osseointegrating protuberances, the anglebetween the longitudinal axes of the osseointegrating protuberances andthe implant axis can vary depending on whether a permanent or removableimplantation is desired. For example, osseointegrating protuberancesthat are parallel with the implant axis are generally more easilyextricated from the bone than those that are oriented at an angle withthe implant axis. In addition, other features, such as threads, can beimplemented to provide the ability to manually extricate the housing.

The osseointegrating protuberances are either formed of or coated withtitanium, a titanium alloy or other material or surface treatment thatencourages or facilitates osseointegration. Preferably, the remainingparts of the housing do not osseointegrate with the bone. For example,the housing may be coated with a material that preventsosseointegration, such as a biocompatible silicone, or may be formedfrom a biocompatible metallic, ceramic and polymeric material.

FIGS. 2A-2C are plan, side and end views of one embodiment ofstimulator/receiver unit 106 introduced above in connection with FIG. 1.In the embodiment shown in FIGS. 2A-2C, stimulator unit 106 has ahousing 200 in accordance with one embodiment of the present invention.In this exemplary application, housing 200 is configured to have mountedtherein electronics and other components (not shown) ofreceiver/stimulator unit 106. As such, a receiver antenna coil isoperatively connected to housing 200. In this exemplary embodiment, acasing 202 is attached to housing 200. Casing 202 is preferably formedby encapsulating the receiver antenna coil in, for example, silicone.

Osseointegrating protuberances in the form of loop members 204A, 204B(collectively and generally referred to herein a loop(s) or loopmember(s) 204) extend from housing 200 to engage bone 206. In thisexemplary application of a stimulator/receiver unit, bone 206 is aregion of a patient's skull such as posterior section of the mastoidbone.

As shown in FIGS. 2A-2C, loop members 204 extend outwardly from anabutting surface 208 of housing 202 to engage bone 206. As a result, thecontour of surface 208 that abuts bone 206 generally follows the contourof the bone in the region of contact. However, given the relativelysmall dimensions of housing 200 and the relatively planar surface of thetarget region of the skull, abutting surface 208 is substantially planarand, as shown in FIG. 2D, resides in and defines a plane 210.

In FIG. 2D, housing 200 is shown spaced apart from the surface of bone206, and oriented for implantation. This and similar orientations is/arereferred to herein as an implant orientation. In other words, whenhousing 200 is oriented relative to bone 206 such that housing 200 canbe brought into contact with bone 206 while maintaining such orientationto implant the device 106, housing 200 is said to be in an implantorientation.

The direction of movement to bring housing 200 into contact with bone206 defines an implant axis 216. Given the relatively planar nature ofsurface 208 of housing 200, implant axis 216 is, in this exemplaryapplication, substantially orthogonal to the imaginary plane 210 definedby surface 208.

When housing 200 is in the implant orientation adjacent to bone 206 loopmembers 204 extend from housing surface 208 toward bone 206. In theembodiment shown in FIG. 2D, loop members 204 extend from a surface 208that abuts bone 206. It should be appreciated, however, that loopmembers 204 can extend from or be coupled to other surfaces of housing200. As shown in FIG. 2D, loop members 204 generally have a longitudinalaxis 212. Loop members 204 extend from housing surface 208 at an angle215 relative to an implant axis 216. Angles 215 as well as the size andshape of loop members 204 are selected to enable loop members 204 toextend into bone 206 and to facilitate the osseointegration of the loopmembers in bone 206. The material that forms or coats protuberances 204also can be selected to achieve a desired degree of osseointegration. Inthe embodiment shown in FIG. 2D, angles 214 are approximately 45degrees. It should be understood, however, that loop members 204 can beat any angle 215 that provides the desired degree of stability of theimplanted device subsequent to sufficient osseointegration. For example,it may be desirable to insure stimulation unit 106 cannot be removedfrom bone 206. By orienting loop members 204 at an angle, bone formationover the loop members provides such a permanent retention in addition tothe osseointegration of loop members 204. In such embodiments, then,angles 215 can range, for example, from 5 to 85 degrees. It should beappreciated, however, than angles 215 need not be within this range, aswill be shown by the embodiments described below. In some suchembodiments, loop members 204 may not be permanently implanted in bone206; that is the implanted device can be extricated from bone 206.

It should also be appreciated that loop members 204 may or may notreside in the same plane. In the embodiment shown in FIGS. 2A-2D, loopmembers 204 reside in the same plane and, as noted, are oriented atopposing angles 215 relative to implant axis 216. In addition toinsuring a more permanent implantation, such an arrangement also insuresthat housing 200 will experience minimal relative lateral shiftingrelative to bone 206.

In FIGS. 2A-2C, and the surface of the patient's skull 206 on placementof housing 200 in a periosteal pocket 214 formed in bone 206. Subsequentto implantation, loops 204 gradually sink into and osseointegrate withbone 206. In some circumstances, the time duration for substantialosseointegration is approximately 40 days. In other circumstances, thetime for osseointegration to occur is more or less than 40 days. Duringosseointegration, housing 200 is drawn toward bone 206. Once abuttingsurface 208 of housing 200 comes into contact with the surface of skull206, the implantable component 200 ceases to sink into skull 206 and isso held in place by loops 204 that have osseointegrated with the bonysurface of the skull.

In accordance with the teachings of the present invention, loop members204 are either made of, or coated with, a material that stimulates theosseointegration process. In one embodiment, loop members 204 are madeof or coated with titanium or a titanium alloy. It should beappreciated, however, that loop members 204 can be made of or coatedwith other materials now or later developed that stimulateosseointegration.

FIGS. 3A-3C are plan, side and end views of another embodiment of animplantable osseointegrating housing 300. FIG. 3D is a schematic endview of housing 300. In this embodiment, housing 300 has a casing 302containing a receiver antenna similar to the embodiment ofstimulator/receiver 106 described above in connection with FIGS. 2A-2D.Housing 300 and casing 302 are implanted in a periosteal pocket 314 inbone 206.

In this embodiment, housing 300 has three (3) studs 304A-304C(collectively and generally referred to herein as stud or studs 304)extending from an abutting surface 308 of the housing. Studs 304 areeither made of, or coated with, a material that stimulates theosseointegration process. In one embodiment, studs 304 are made of orcoated with titanium or a titanium alloy. It should be appreciated,however, that studs 304 can be made of or coated with other materialsnow or later developed that stimulate osseointegration.

Referring to FIG. 3D, abutting surface 308 of housing 300 generallydefines a plane 310. Each stud 304 has a longitudinal axis 312 which issubstantially parallel with implant axis 316. Studs 304 osseointegratewith the bony surface of skull 206 over time. However, due to theorthogonal orientation of studs 304 and bone 206, the orientation ofstuds 304 does not prevent housing 300 from being lifted away from thebony surface of skull 206 in a direction parallel with implant axis 312.To extricate studs 304, the bonds formed during osseointegration must besevered. Thus, it is preferential that studs 304 do not includeadditional integrating features such as apertures. It should beappreciated, however, that studs 304 serve to prevent at leastsubstantial lateral movement of housing 300 relative to bone 306. Thisand similar embodiments of osseointegrating protuberances 304 may beutilized in those applications in which it may be necessary to replacethe device, access housing 300 or otherwise manipulate, maintain, repairor replace an implantable component.

FIGS. 4A-4C are plan, side and end views of another embodiment of animplantable osseointegrating housing 400. In this embodiment, housing400 has a casing 402 containing a receiver antenna similar to theembodiments of stimulator/receiver 106 described above in connectionwith FIGS. 2A-3D. Housing 400 and casing 402 are implanted in aperiosteal pocket 414 in bone 206, although, as in all embodiments,housing 400 can be implanted in other beds or wells, or simply on thesurface of bone 206.

In this embodiment, housing 400 has two (2) osseointegrating protrusionsin the form of threaded shafts 404A-404B (collectively and generallyreferred to herein as screw or screws 404) extending from a surface 409adjacent to abutting surface 408 of the housing 400. In this exemplaryembodiment, shafts 404 are threadedly mounted to respective flanges405A, 405B. Flanges 405 extend outwardly from sidewall surfaces 409 ofhousing 400. It should also be appreciated that other arrangements arepossible where flanges 405 extend from a different location on housing400.

In the embodiment shown in FIGS. 4A-4C, each threaded shaft 404 is ascrew having a slot in the head thereof to receive a tool, such as ascrewdriver. On implantation, such screws 404 are preferably notinserted or screwed into the bony surface of bone 206. Rather, thedistal end of each screw is positioned so as to abut the bony surfaceunder pressure applied by the placement of housing 400 in periostealpocket 414 adjacent the bony surface. Over time, screws 404 willosseointegrate with the bony surface. Should it becomes necessary toremove housing 400, screws 404 can be unscrewed from bone 206 using ascrewdriver and the housing can then be lifted away from the bonysurface. The screws 404 may be surgical screws and preferably have a lowprofile so they do not cause tissue erosion.

Threaded shafts 404 are either made of, or coated with, a material thatstimulates the osseointegration process. In one embodiment, threadedshafts 304 are made of or coated with titanium or a titanium alloy. Itshould be appreciated, however, that threaded shafts 404 can be made ofor coated with other materials now or later developed that stimulateosseointegration. Also, flanges 405 may be formed from titanium or atitanium alloy, and may be attached to a titanium housing 400 by, forexample, welding. Alternatively, flanges 405 may be integrally formedwith housing 400. It should also be appreciated that the flanges 405 maybe made from a plastic or elastomeric materials bonded to the implanthousing 400. For example, it may be possible to extend a silicone rubbercoating of the implant housing 400 to create a silicone rubber flangewhich secured to bone 206 via screws 404. Further, it may be possible toembed a plastic material such as PTFE or polyurethane within thesilicone rubber coating of implant housing 400 to form a flange, or evenattach such a device to the housing via a mechanical interlock. It mayalso be possible to make flange 405 of a composite or combination ofmaterials. For example, a Dacron mesh may be used as a reinforcingstructure to strengthen the silicone rubber coating. PTFE, polyurethaneor carbon fibre materials may also be used as a reinforcing member toform flanges 405.

By providing a flange 405 made from a plastic or elastomeric material itmay be possible to allow the surgeon to remove or cut-off the flangeduring the surgical procedure should they not wish to use such afixation method, resulting in the fixation mechanism of the presentinvention being an optional feature. Such a flange would also be easierto form and alter the shape thereof to more appropriately conform to theshape of certain bones, such as a recipient's skull. Further, a flangemade from a plastic or elastomeric material is softer than a metallicflange and will therefore be less prone to causing tissue erosion. Stillfurther, the depicted flanges could be removably mounted to the housingso allowing them to be removed if not required.

Alternatively, another aspect of the present invention includes that ofa housing for an implantable device to be secured for mounting to apatient's bone is disclosed. The housing can include a surface having anabutting portion configured to abut the bone when the housing isimplanted in the patient, the abutting portion defining a housing axisorthogonal to the surface; and at least one osseointegratingprotuberance extending from the surface of the housing; the at least oneprotuberance being adapted to abut the patient's bone; and the at leastone protuberance having a substantially smooth shaft. Material for thesurface of the housing can include, e.g., at least one of abiocompatible metallic, ceramic and polymeric material.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

What is claimed is:
 1. An implantable device for mounting to a patient'sbone, the device comprising: a housing including a surface having anabutting portion configured to abut the bone when the device isimplanted in the patient, the abutting portion defining a housing axisorthogonal to the surface; and at least one stud extending from thesurface of the housing; the at least one stud being adapted to abut thepatient's bone; and the at least one stud having a substantially smoothshaft.
 2. The implantable device of claim 1, wherein the at least onestud includes: first and second studs extending from the surface; thefirst and second studs each being adapted to abut the patient's bone;and the first and second studs each having a substantially smooth shaft.3. The implantable device of claim 1, wherein: the at least one stud isconfigured to prevent only substantial relative lateral movement betweenthe housing and the patient's bone.
 4. The implantable device of claim1, wherein: the at least one stud is formed of one of titanium and atitanium alloy.
 5. The implantable device of claim 1, wherein the atleast one stud includes: a core member; and a coating on the coremember, the coating being one of titanium and a titanium alloy.
 6. Theimplantable device of claim 1, wherein: the at least one stud has asurface treatment that encourages osseointegration.
 7. The implantabledevice of claim 1, wherein: the surface of the housing is coated with amaterial configured to prevent osseointegration.
 8. An implantablecomponent of a tissue stimulating prosthesis, the implantable componentcomprising: a housing including a surface having an abutting portionconfigured to abut a patient's bone when the housing is implanted in thepatient, wherein the abutting portion defines a housing axis orthogonalto the surface; and one or more components of the prosthesis mounted inthe housing; at least one stud extending from the surface of thehousing; the at least one stud being adapted to abut the patient's bone;and the at least one stud having a substantially smooth shaft.
 9. Theimplantable component of claim 8, wherein the at least one studincludes: first and second studs extending from the surface; the firstand second studs each being adapted to abut the patient's bone; and thefirst and second studs each having a substantially smooth shaft.
 10. Theimplantable component of claim 8, wherein: the at least one stud isconfigured to prevent only substantial relative lateral movement betweenthe housing and the patient's bone.
 11. The implantable component ofclaim 8, wherein: the at least one stud is formed of one of titanium anda titanium alloy.
 12. The implantable component of claim 11, wherein theat least one stud includes: a core member; and a coating on the coremember, the coating being one of titanium and titanium alloy.
 13. Theimplantable component of claim 8, wherein: the at least one stud has asurface treatment that encourages osseointegration.
 14. The implantablecomponent of claim 8, wherein: the tissue stimulating prosthesis is acochlear implant.
 15. The implantable component of claim 14, wherein:the one or more components mounted in the housing are configured tofunction as a stimulator unit of the cochlear implant.
 16. A method forimplanting an implantable device having a housing with an abuttingsurface and at least one stud extending from the housing, the methodcomprising: forming a pocket in a patient's bone to receive the housing;positioning the housing in the pocket; and simultaneously withpositioning the housing in the pocket, positioning the at least one studso as to be in direct contact with a surface of the patient's boneforming the pocket.
 17. The implantable device of claim 1, wherein theat least one stud is integral with at least a portion of the housing.18. The implantable component of claim 8, wherein the at least one studis integral with at least a portion of the housing.
 19. The method ofclaim 16, wherein the at least one stud projects below a surface of thepocket when positioned in the pocket.
 20. The method of claim 16,wherein the at least one stud comprises a plurality of studs.